Abstract
Candida albicans biofilms display markedly increased antifungal resistance, and the underlying mechanisms remain unclear. This study investigated the signature profiles of C. albicans planktonic cells and biofilms in response to caspofungin (CAS) by mass spectrometry-based shotgun proteomics. We found that C. albicans biofilms were twofold more resistant to CAS with reference to planktonic cells. Notably, 9.6% of C. albicans biofilm cells survived the lethal treatment of CAS (128 μg/ml), confirmed by LIVE/DEAD staining, confocal laser scanning microscopy (CLSM) and scanning electron microscopy analyses. The responses of C. albicans planktonic cells and biofilms to CAS treatment at respective minimum inhibitory concentrations (MICs) were assessed by high-throughput proteomics and bioinformatics approaches. There were 148 and 224 proteins with >twofold difference identified from the planktonic cells and biofilms, respectively. CAS treatment downregulated several cell wall- and oxidative stress-related proteins. Whereas, CAS-induced action was compensated by markedly increased expression of many other proteins involved in cell wall integrity and stress response (e.g., heat shock proteins). Moreover, considerable expression changes were identified in metabolism-associated proteins like glycolysis, tricarboxylic acid (TCA) cycle and ATP biosynthesis. Importantly, various key proteins for cell wall integrity, stress response and metabolic regulation (e.g., PIL1, LSP1, HSP90, ICL1, and MLS1) were exclusively enriched and implicated in C. albicans biofilms. This study demonstrates that C. albicans biofilms undergo highly complicated yet complex regulation of multiple cellular pathways in response to CAS. Signature proteins essential for modulating cell wall integrity, stress response and metabolic activities may account for the antifungal resistance of C. albicans biofilms.
Highlights
Candida albicans remains the predominant pathogen for various refractory superficial and systemic infections with high morbidity and mortality (Seneviratne et al, 2015; Lohse et al, 2018)
The effects of CAS exposure on C. albicans biofilms at different concentrations were further examined by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM)
Antifungal susceptibility testing demonstrated that C. albicans biofilms were more resistant to CAS with reference to the planktonic counterparts
Summary
Candida albicans remains the predominant pathogen for various refractory superficial and systemic infections with high morbidity and mortality (Seneviratne et al, 2015; Lohse et al, 2018). It is a frequent colonizer on tissue surfaces and implanted medical devices, forming adherent biofilms capable of withstanding currently limited arsenal of antifungals. The echinocandins represent a novel class of antifungals that exert fungicidal activity by noncompetitively inhibiting β1,3-glucan synthase required for fungal cell wall biosynthesis (Denning, 2003). C. albicans biofilms are 2–20 times more resistant to CAS as compared to its planktonic form (Tobudic et al, 2010; Taff et al, 2013)
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